Method for cooling turbine stators and cooling system for implementing said method

ABSTRACT

A method and system for cooling turbine engine turbines, the system includes: at least one pair of parts to be cooled, the pair including a stator upstream from the rotor valve, and a sealing ring mounting a downstream movable blade rotor that is adjacent to the stator; a turbine casing; and an outlet path. The system further includes: at least one opening in the casing facing at least one part to be cooled; and an air circuit producing a forced convection in connection with the parts and at least one downstream outlet in the path so as to draw in and transport an ambient air flow.

The invention relates to a method for cooling stators, distributors or rings of gas turbines equipping the aircraft propelling turbo-machines, in particular helicopters, as well as a cooling system for implementing the method.

The thermodynamic cycles of the turbo-machines are higher and higher in temperature, which requires a cooling extended to the stator portions of the turbine: the stationary vanes of the distributor of the turbine, as well as the smooth or sealing ring support (designated hereinunder by ring support) of the movable blades or rotor. The air is then introduced across the vanes of the distributor and then above the rotor ring. The air is then reintroduced in the outlet path.

Now, the outlet nozzle presents at low speeds a recovering coefficient (Cp) being able to reach negative values, which results in an inversion of the pressure deviation between the atmosphere and the outlet plan of the turbine. Hot air reintroductions can then occur by exhaust and prevent the cooling of the stator.

Furthermore, the use of cooling air being tapped at the level of the compressor has a performance cost, as it does not any longer contribute to the motive work.

The invention aims at remedying such disadvantages by proposing an ambient air aspiration at the level of the stator to be cooled.

More precisely, the invention relates to a method for cooling turbine parts of an engine presenting at the exhaust an architecture with a positive Cp on the whole operating speeds, for which a cooling is desired, consisting in tapping an ambient air flow by aspiration at the level of at least one part to be cooled, followed by a crossing producing a forced convection in connection with said part, and then by a downstream air reintroduction in the outlet path.

The terms “upstream” and “downstream” refer to the air flow direction in the engine and the terms “internal”, respectively “external, refer to localizations “viewed from”, respectively “in the direction of” the turbine rotation axis.

Such method is particularly efficient in the case of configurations of turbines or engines being able to define an outlet depression being sufficient to provide a Cp staying positive on a set of operating speeds. That is the case including for:

-   -   mono-stage turbines operating at the same expansion rate as a         bi-stage turbine, which allows an outlet static pressure         substantially smaller than with a bi-stage turbine to be         obtained;     -   engines with axisymmetric nozzles used in particular with a         through-shaft architecture.

According to preferred embodiments:

-   -   cooling being intended for at least one pair of parts comprising         an upstream stator and a downstream ring support being adjacent         to the stator, such cooling is performed in a serial mode with a         successive circulation of a same air flow in both parts, in a         parallel mode with circulations being independent of the air         flow in each of the parts or in a mixed mode with the successive         circulation of a same flow and a circulation being independent         in the second part by tapping ambient air at the level of the         upstream stator for serial and mixed cooling, and at the level         of each part for parallel and mixed cooling;     -   the downstream reintroductions in the outlet path are         implemented with parallel exhausts;     -   the tapped air is also contacted with at least one engine part         to be cooled as, for example, the holding lock of the ring         support on the arm of the casing.

The invention also aims at a system for cooling turbines of turbo-machines comprising at least one distributor upstream stator with stationary vanes, a ring support for movable blades, a turbine casing and an outlet path, the system being able to implement the above mentioned method. Such system comprises an opening in the casing facing at least one part to be cooled, a forced air circulation in connection with such part and at least one downstream outlet in the path.

According to particular embodiments:

-   -   an opening is formed in the casing facing an air circulation         inlet in each vane of the distributor to be cooled, such         circulation being performed by a radial circuit comprising at         least two channels, as well as an air outlet in the outlet path         of the turbine;     -   an axisymmetric cavity is provided between the two channels so         as to homogenize the pressure of the air flow and to implement a         better cooling of the stationary vanes;     -   the distributor and the sealing ring support of the rotor of a         turbine are serially cooled by a communication channel in outlet         of a distributor vane, which channel opens into a cavity in         radial connection with the external side of the ring support,         and then toward the outlet path of the turbine through at least         one orifice provided in the ring support;     -   the ring support presents at least one upstream hook being able         to enclose bladed flanges, being sectored or not, of the casing         and the distributor so as to form the communication channel;     -   the channel of each vane of the distributor comprises an         extension directly opening into the cavity to form the         communication channel;     -   the cooling being performed in a parallel mode, the radial         circuit of the vane of the distributor opens facing a channel         inlet arranged in the ring support of the rotor to cross it up         to the outlet path, and an orifice is formed in the casing         opposite the ring support so as to tap an ambient air flow by         drawing in and form a parallel air circulation circuit crossing         the cavity and the ring support by an outlet orifice;     -   a ring-shaped perforated metal sheet is provided in the cavity         of the cooling circuit of the ring support so as to improve the         thermal exchange with the air being tapped;     -   the cooling is performed in serial and/or parallel mode by a         combination of the above mentioned serial or parallel air         circulations;     -   the air circulation is implemented by blading the structure of         the stator vanes and/or the casings participating in such         circulation;     -   at least one air circuit is equipped with non-return air valves         that could be located at the level of the openings arranged in         the casing.

The invention applies in particular to mono-stage turbines, and to the architecture of through-shaft engines, which allows advantageously the use of axisymmetric nozzles presenting particularly favorable CP curves on the whole speeds.

Other characteristics and advantages of the invention will appear with the reading of the detailed description of exemplary embodiments hereinunder, in reference to the accompanying FIGS. representing respectively:

FIG. 1, a partial section view of an exemplary serial cooling circuit of a stator distributor and a sealing ring support of a turbine rotor in a turbo-machine;

FIGS. 1 a and 1 b, an enlargement of the assembly between the distributor and the casing by a hook and a partial section view along I-I of FIG. 1 a at the level of such assembly;

FIG. 1 c, a partial section view of an axisymmetric cavity located between the two cooling channels;

FIG. 2, the example of the FIG. 1 with a doubled upstream sealing and an alternative air circulation channel in the distributor;

FIG. 3, a partial section view of an exemplary serial cooling circuit of a distributor and a ring support in the rotor with no heel; and

FIG. 4, a partial section view of an exemplary parallel cooling circuit of a turbine with movable blades without any heel.

The terms “internal” or “external” qualify an element viewed from the side of the rotation axis of the turbine or from the side opposite to such axis. Furthermore, identical reference annotations on the FIGS. refer to identical or equivalent elements.

Referring to FIG. 1, the turbine 1 consists specifically in a casing 3, an air distribution stator or distributor with stationary vanes 7, a sealing ring support 9 for movable blades 11, and an outlet path 13 for an access to the nozzles (not represented). The casing 3 fastens the position of the distributor and the ring support by support arms 3 a, 3 b and 3 c. The air under cowl is drawn in under the form of a flow Fs by depression across an intake orifice 15 of the casing 3 and up to the outlet path 13 thru the distributor 7 and the ring support 9.

The orifice 15 is arranged facing an air inlet opening 17 provided on one end of a first radial circulation channel 19 inside the distributor 7. The upstream sealing of the distributor 7 on the casing 3 is provided by a gasket 20 between the first upstream arm 3 a of the casing 3 and an upstream rim 7 r of the distributor 7.

A central radial wall 22 separates the first channel 19 from a second circulation channel 24, the channels being also bordered by the leading 7 a and trailing 7 f edges of the vanes of the distributor 7. Both channels communicate through a cavity 25 allowing the flow Fs to circulate from the first to the second channel in opposite directions. In an alternative solution, shown on FIG. 1 c, a part 25 a is fastened by any known means (screw, welding) to the end of the vane 7 so as to provide the transition between the channels 19 and 24. The inside of this part is machined so as to form an axisymmetric cavity 25 b located between the two channels 19 and 24 for homogenizing the pressure of the air flow Fs and thereby obtaining a better cooling of the stationary vanes 7. Such insert configuration also favors the manufacture of the vane 7, since the internal radial end thereof is opened. Air flow perturbations 28, of the so-called “trombone” type, are provided inside the channels so as to increase the thermal transfers.

At the radial end of the second channel 24, the flow Fs enters and circulates, causing a forced convection in a cavity 26 located between the casing 3 and the external side Fe of the ring support 9. A radially external ring-shaped sheet 30 is made integral, at the level of the ends thereof, with the stationary ring support 9. As more particularly illustrated on FIGS. 1 a and 1 b, the connection between the channel 24 and the cavity 26 is made by bladings 7 l and 3 l formed in the arms 7 b and 3 b, respectively, of the distributor 7 and the casing 3. Such flanges are held in a hook 32 forming the upstream end of the ring support 9. Perforations 30 a are arranged in the ring-shaped sheet so as to form a ring-shaped impact jet 30 with increased air speed so as to facilitate the thermal transfer between the ring support 9 and the cavity 26. The ring-shaped sheet is made integral, at the upstream end thereof, with a radial side of the hook 32.

In the illustrated example, the movable blades 11 are equipped with heels 34 on their external ends, facing an abradable honeycomb material 36. Such abradable material is made integral with the internal side Fi of the ring support 9. The downstream end of the ring support 9, with which the downstream end of the ring-shaped sheet 30 is made integral, and the downstream flange 3 c of the casing 3 are held tightened by a lock 38. Such material allows the clearances to be limited between the movable blades 11 and the sealing ring support 9 upon expansion of the blades, in particular at high speeds: the lips 34 a of the heel 34 can then enter the material 36 with no degradation so as to provide the sealing between the rotor and the ring.

The flow Fs goes up by depression, still providing a forced convection, toward the downstream end of the ring support, and then is drawn in by an opening 40 arranged on the ring support 9. Advantageously, the thermal transfer can be improved by forced convection on a rough surface formed on the ring-shaped sheet 30. The flow exhausts then in the path 13 through passages 42 downstream from the movable blades 11.

Alternatively, on the one side, the upstream sealing gasket 20 of the stationary vane 7 may be a lip joint in “w” and, on the other side, the ring support may be present under a continuous annular form or in the form of annular sectors (sectoring).

In an alternative, such as represented on FIG. 2, the upstream sealing of the distributor 7 is doubled: a place for a second gasket 44 is arranged by the presence of a shoulder 46, being formed on a protuberance of the leading edge 7 a, facing a groove 48 arranged in the upstream flange 3 a of the casing 3.

Moreover, FIG. 2 shows an alternative for the flow passage of the second cooling channel 24 of the distributor 7 toward the cavity 26. Such passage is obtained by an extension 24 p of the channel 24. Such extension is going, while bending and tapering in the illustrated example, directly to open into the cavity 26 through an opening 50 formed in the flange 3 b of the casing 3.

According to another alternative, being illustrated on FIG. 3, the movable blades do not have any heel. The ring support 9 stays at a sufficient distance from the edge 11 b of the blade 11 so as to prevent any contact upon thermal expansions of the movable blades 11. Moreover, an abradable material layer 37 may be projected on the ring support so as to provide the sealing at the top of the blades. Such configuration has this advantage to be able to have a cavity 26 of a larger volume and, thus, of a larger quantity of air flow Fs, allowing for a better thermal transfer with the external side Fe of the ring support, before exhausting through the opening 26 toward the outlet path 13. A perforated ring-shaped sheet 30 can also be provided within such cavity, for example by welding at mid-height. Moreover, the mounting of the ring support 9 is simplified by being held on the casing 3 with the help of a flange 33.

FIG. 4 illustrates an exemplary cooling system in a parallel mode according to the invention from a configuration of movable blades 11 with no heel. Such cooling system comprises two air flow circulation circuits Fs and Fs′ being independent. The first circuit relates to the cooling of the distributor 7 from the aspiration through the opening 15 of the carter 3 and the air flow circulation Fs in the channels 19 and 24, as described in reference to FIGS. 1 and 2 up to the first blading 7 l formed in the arm 7 b of the distributor 7. No blading is formed herein in the flange 3 b of the casing 3. A direct outlet channel 52 is formed in the ring support 9 opposite the blading 7 l and opens into the outlet path 13. At the outlet of the blading 7 l, the air of the flow Fs then enters the inlet 53 of the channel 52 to go out in the path 13.

The second air circuit is implemented from a second orifice 54 formed in the casing 3 at the level of the ring support 9. By depression, the air flow Fs′ crosses the cavity 26 and goes out through a second opening 56 made in the ring support 9, in parallel with the outlet of the channel 52. Those circuits thus contribute to the cooling of the ring support 9.

The invention is not limited to the exemplary embodiments described and represented. Thus, the air circulations in connection with the stator and with the sealing ring support can be totally independent by providing an outlet from the radial channel 24 of the vanes 7 in the stator directly in the path 13. Furthermore, it is possible to provide a number of radial channels higher than two in the vanes of the distributor, several openings in the casing at the level of each stator, distributor or ring support, or still arrangements of the distributor or the ring support on the casing by any convenient means known from the man of the art (crimping, hooping, welding, etc.). Furthermore, the number of distributors and rotors is not limited to one, but corresponds to any turbine targeted by the present invention. 

1-10. (canceled)
 11. A method for cooling turbine parts of an engine presenting at exhaust an architecture with a positive Cp on whole operating speeds, for which a cooling is desired, provided for at least one pair of parts including an upstream stator and a sealing ring support of downstream movable blades adjacent to the stator, the method comprising: tapping an ambient air flow by aspiration at a level of at least one part to be cooled; then a crossing producing a forced convection in connection with the part; and then a downstream air reintroduction in an outlet path, wherein cooling is performed in a serial mode with a successive circulation of same air flow in both parts, in a parallel mode with circulations being independent of the air flow in each of the both parts, or in a mixed mode with successive circulation of a same flow in the both parts, and independent circulation of a second flow in the second part by tapping ambient air at a level of the upstream stator for serial and mixed cooling, and of each part for parallel and mixed cooling.
 12. The cooling method according to claim 11, wherein the downstream reintroduction in the outlet path is implemented with parallel exhausts.
 13. A system for cooling turbines of turbo-machines for implementation of the method according to claim 11, comprising: at least one pair of parts to be cooled of a distributor upstream stator with stationary vanes and a sealing ring support of a rotor with downstream movable blades adjacent to the stator, a turbine casing and an outlet path, at least one opening in the casing facing at least one part to be cooled, a forced air circulation in connection with the one part and at least one downstream outlet in the path, wherein the cooling of the distributor and the sealing ring support of the turbine rotor is serially performed; and a communication channel in an outlet of a vane of the distributor opening into a cavity in radial connection with an external side of the ring support, and then toward the outlet path of the turbine through at least one orifice provided in the ring support.
 14. The cooling system according to claim 13, wherein an opening is formed in the casing facing an air circulation inlet in each vane of the distributor to be cooled, circulation being performed by a radial circuit comprising at least two channels, and an air outlet in the outlet path of the turbine.
 15. The cooling system according to claim 14, wherein an axisymmetric cavity is provided between the two channels so as to homogenize pressure of the flow and to implement a better cooling of the stationary vanes.
 16. The cooling system according to claim 15, wherein the ring support includes at least one upstream hook configured to enclose bladed flanges of the casing and the distributor vane so as to form the communication channel.
 17. The cooling system according to claim 16, wherein the circulation channel of each vane of the stator comprises an extension directly opening into the cavity to form the communication channel.
 18. The cooling system according to claim 13, wherein a ring-shaped perforated metal sheet is provided in the cavity of the cooling circuit of the ring.
 19. A system for cooling turbines of turbo-machines to implement the method according to claim 11, comprising: at least one pair of parts to be cooled of a distributor upstream stator with stationary vanes and a sealing ring support of a rotor with downstream movable blades adjacent to the stator, a turbine casing and an outlet path, at least one opening in the casing facing at least one part to be cooled, a forced air circulation in connection with the one part and at least one downstream outlet in the path, wherein the cooling is performed in a parallel mode, the radial circuit of the vane of the distributor opening opposite a channel inlet arranged in the ring support of the rotor so as to cross it up to the outlet path, and an orifice being formed in the casing facing the ring support to tap an ambient air flow by aspiration and form a parallel air circulation circuit crossing the cavity and the ring support through an outlet orifice.
 20. A system for cooling turbines of turbo-machines to implement the method according to claim 11, comprising: at least one pair of parts to be cooled of a distributor upstream stator with stationary vanes and a sealing ring support of a rotor with downstream movable blades adjacent to the stator, a turbine casing and an outlet path, at least one opening in the casing facing at least one part to be cooled, a forced air circulation in connection with the one part and at least one downstream outlet in the path, wherein the cooling is performed in a mixed mode through a successive circulation of a same flow in both parts for a cooling in a serial mode, and through a flow circulation being independent in the second part for a cooling in a parallel mode. 